Bisaminothiophenol compound, process for producing the same and curing agent for fluorine-containing elastomer comprising the same

ABSTRACT

2,2-bis(4-aminophenyl)hexafluoropropane is allowed to react with potassium thiocyanate and bromine to obtain 2,2-bis(5-amino-4,6-benzothiazolyl)hexafluoropropaneo which is allowed to further react successively with potassium hydroxide and hydrochloric acid to obtain 2,2-bis(4-amino-3-mercapto-phenyl)hexafluoropropane, which is a novel compound applicable as a curing agent for a fluorine-containing elastomer having CN groups as cross-linkable groups.

This is a Divisional of application Ser. No. 08/550,870 filed Oct. 31,1995.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a bisaminothiophenol compound, and moreparticularly to a bisaminothiophenol compound effectively applicable asa curing agent for a fluorine-containing elastomer having nitrile groupas cross-linkable group.

2. Related Art

The following bisaminothiophenol compounds are known and are used asstarting materials for polybenzothiazole compounds as heat-resistantresin, etc. ##STR1##

SUMMARY OF THE INVENTION

An object of the present invention is to provide a novelbisaminothiophenol compound, which can be effectively applied as acuring agent for fluorine-containing elastomer having nitrile group ascross-linkable group.

According to the present invention, there is provided a novelbisaminothiophenol compound represented by the following general formulaI!: ##STR2## wherein Rf is a perfluoroalkylidene group of C₁ to C₁₀,which can take a salt form, such as hydrochloride, hydrobromide,sulfate, borate, carboxylate, etc.

DETAILED DESCRIPTION OF THE INVENTION

The present bisaminothiophenol compound can be produced according to awell known synthesis process through a series of the following steps:##STR3##

Reaction of III!→ II!:

A solution of bromine in glacial acetic acid is dropwise added to asolution of a bisaminophenyl compound III! and an alkali metalthiocyanate such as potassium thiocyanate or sodium thiocyanate inexcess of an equimolar amount to that of bisaminophenyl compound III! inglacial acetic acid at room temperature with stirring and then water isadded thereto. The mixture is heated up to the boiling point and thencooled and filtered. Sodium hydrogen carbonate is added to the filtrateto obtain a bisaminobenzothiazole compound II! as precipitates. It seemsthat bromine acts as an oxidizing agent to make the thiocyanate additionreaction with the aromatic nucleus, followed by a nucleophilicring-closing reaction between the thiocyano group and the amino group.

Generally. 2,2-bis(4-aminophenyl)hexafluoropropane can be used as thebisaminophenyl compound III!. Besides,1,2-bis(4-aminophenyl)tetrafluoroethane, etc. can be used.

Reaction of II!→ I!:

The thus obtained bisaminobenzothiazole compound II! is added to anaqueous solution of an alkali metal hydroxide such as potassiumhydroxide or sodium hydroxide in an inert gas atomosphere at atemperature of about 110° to about 130° C., and then the mixture isslowly heated to about 260° C. to conduct reaction until generation ofammonia is ceased. Then, the temperature is lowered down to about 200°C. After addition of water thereto, the reaction mixture is cooled downto room temperature. Then, an aqueous dilute solution of an inorganicacid such as a concentrated hydrochloric acid is added to the reactionmixture to make pH 6, and then glacial acetic acid is added thereto toobtain a bisaminothiophenol compound I! as precipitates.

The thus obtained bisaminothiophenol compound or its salt can be used asa curing agent for a fluorine-containing elastomer having CN group ascross-linkable group.

The fluorine-containing elastomer for use in the present inventionincludes a terpolymer of tetrafluoroethylene. perfluoro(lower alkylvinyl ether) or perfluoro(lower alkoxy-lower alkyl vinyl ether) and asmall amount (i.e. about 0.1 to 5% by mole on the basis of theterpolymer) of perfluoro unsaturated nitrile compound.

The perfluoro unsaturated nitrile compound includes, for example, thefollowing compounds:

CF₂ ═CFO(CF₂)nOCF(CF₃)CN (n: 2˜5)

CF₂ ═CF OCF₂ CF(CF₃)!nO(CF₂)mCN (n: 1˜2, m: 1˜4)

CF₂ ═CF OCF₂ CF(CF₃)!nCN (n: 1˜5)

CF₂ ═CFO(CF₂)nCN (n: 1˜10)

About 0.1 to about 5 parts by weight, preferably about 1 to about 3parts by weight, of the present bisaminothiophenol compound is added asa curing agent to 100 parts by weight of the fluorine-containingelastomer having CN group as cross-linkable group due to theincorporation of the perfluoro unsaturated nitrile compound bycopolymerization. The fluorine-containing elastomer can further containnecessary additives such as a filler, a reinforcing agent, a stabilizer,a plasticizer, a lubricant, a processing aid, etc. besides thebisaminothiophenol compound. The resulting mixture is kneaded in a rollmill or the like and then subjected to a primary vulcanization (pressvulcanization) at a temperature of about 160° to about 250° C. for about30 to about 60 minutes and then to a secondary vulcanization (ovenvulcanization) at a temperature of about 200° to about 300° C. for about10 to about 50 hours, preferably in an inert gas atmosphere.

According to the present invention, a novel bisaminothiophenol compoundeffectively applicable as a curing agent for a fluorine-containingelastomer having CN group as cross-linkable group can be provided.

PREFERRED EMBODIMENTS OF THE INVENTION

The present invention will be described in detail below, referring toExamples.

EXAMPLE 1

A solution containing 92.8 g (0.58 moles) of bromine in 20 ml of glacialacetic acid was dropwise added to a solution containing 80 g (0.24moles) of 2,2-bis(4-aminophenyl)-hexafluoropropane and 120 g (1.24moles) of potassium thiocyanate in 280 ml of glacial acetic acid withstirring over one hour. After the dropwise addition, the mixture wasstirred for further 2 hours and left standing overnight. Then, 1 literof water was added thereto, and the mixture was heated to the boilingpoint and then cooled and filtered.

Sodium hydrogen carbonate was added to the filtrate, and the resultingprecipitates were recovered by filtration, washed with water and dried,whereby 102 g of desired2,2-bis(5-amino-4,6-benzothiazolyl)hexafluoropropane was obtained(yield: 95%).

Melting point: 262°˜266° C.

Elemental analysis (C₁₇ H₁₀ F₆ N₄ S₂): Calculated; C 45.53%, H 2.33%, F25.45%, N 12.50%, S 14.28% Found; C 45.23%, H 2.35%, F 24.87%, N 11.74%,S 13.80%

Mass spectrum: 448(relative intensity 86)M⁺ 379(100) M--CF₃ !⁺ 310(15)M--2CF₃ !⁺

¹⁹ F NMR (δ: DMSO): -15.2(s) (CF₃ COOH base)

¹ H NMR (δ: DMSO): H(1), H(2)=6.32 ppm(AB q.); J_(AB) =7.9 Hz; H(3)6.72ppm(br. s.); H(4)=6.8 ppm(br. s.); H(1):H(2):H(3):H(4)=1:1:1:2.

EXAMPLE 2

120 g (2.14 moles) of potassium hydroxide and 16 ml of water werecharged into a round bottom flask and heated at 120° C. in an argonatmosphere while stirring the mixture until potassium hydroxide wasdissolved into water. Then, 44.8 g (0.1 mole) of2,2-bis(5-amino-4,6-benzothiazolyl)hexafluoropropane obtained in Example1 was added thereto also in the argon atmosphere with stirring, and themixture was slowly heated up to 250° C., and then stirred for further 20minutes. Then, the mixture was heated up to 260° C. and can kept at thattemperature for about 10 minutes until generation of ammonia wascompletely ceased to conduct the reaction. Then, the reactiontemperature was lowered down to 200° C. and 600 ml of deaerated waterwas slowly added thereto. Then, the mixture was cooled down to 15° C. Anaqueous dilute solution containing 240 ml of concentrated hydrochloricacid in 240 ml of deaerated water was added thereto to make pH 6, andthen 40 ml of glacial acetic acid was slowly added thereto. Theresulting precipitates were recovered by filtration, washed with waterand dried, whereby 37 g of2,2-bis(4-amino-3-mercaptophenyl)hexafluoropropane was obtained as theultimate product (yield: 93%).

Melting point: 85° C.

Elemental analysis (C₁₅ H₁₂ F₆ N₂ S₂): Calculated; C 45.23%, H 3.01%, F28.64%, N 7.03%, S 16.08% Found; C 45.03%, H 2.88%, F 25.37%, N 6.79%, S15.98%

Mass spectrum: 398M⁺, 364 M--H₂ S!⁺, 329 M--CF₃ !⁺, 295 M--H₂ S--CF₃ !⁺

¹⁹ NMR (δ: DMSO.d₆): -14.55 ppm(s) (CF₃ COOH base)

¹ H NMR (δ): H(1), H(2)=6.05 ppm(AB q.); J_(AB) =9 Hz; H(HS)=4.8 ppm;H(H₂ N)=6.14 ppm.

EXAMPLE 3

200 ml of distilled water, 3.3 g of ammonium perfluoro-octanoate and 2.3g of KH₂ PO₄, were charged into a stainless steel autoclave having a netcapacity of 500 ml, and the gas inside the autoclave was replaced with anitrogen gas. The autoclave was subjected to pressure reduction andcooled down to 0° C. Then, the following compounds were successivelycharged into the autoclave:

    ______________________________________                                        Perfluoro(5-cyanopentyl vinyl ether)  CNVE!                                                             6 g                                                 Perfluoro(methyl vinyl ether)  FMVE!                                                                   60 g                                                 Tetrafluoroethylene  TFE!                                                                              36 g                                                 ______________________________________                                    

Then, the autoclave was heated to 60° C., and then 10 ml of an aqueoussolution containing 0.15 g of sodium sulfite and 10 ml of an aqueoussolution containing 1.10 g of ammonium persulfate were charged theretoto conduct polymerization reaction for 16 hours.

After the end of the reaction, unreacted gases were purged from theautoclave to recover an aqueous latex. Then, the aqueous latex was keptin a refrigerator at -30° C. for 24 hours for freezing. Afterdefreezing, the solidified polymer was washed with 10% ethanol at 50° C.and dried under reduced pressure at 80° C. for 6 hours, whereby 75 g ofterpolymer was obtained (yield: 74%). As a result of infrared absorptionanalysis CN group absorption was observed at 2266 cm⁻¹ and it was foundthat the terpolymer had a composition of 1.0 mol. % CNVE, 57 mol. % FMVEand 42 mol. % TFE.

The following components were kneaded through a double roll rubber milland subjected to primary vulcanization at 160° C. for 30 minutes andthen to secondary vulcanization at 230° C. in a nitrogen gas atmospherefor 22 hours:

    ______________________________________                                        Terpolymer            100 parts by weight                                     Bisaminothiophenol of Example 1                                                                     1 parts by weight                                       MT carbon black       5 parts by weight                                       ______________________________________                                    

The thus obtained vulcanization product had the following normal stateproperties as a result of measurements according to JIS K-6301:

    ______________________________________                                        Hardness (JIS-A)      72                                                      100% modulus          52 kg/cm.sup.2                                          Tensile strength     148 kg/cm.sup.2                                          ______________________________________                                    

It was found that the present bisaminothiophenol compound was useful asa curing agent for a fluorine-containing elastomer having CN group ascross-linkable group.

What is claimed is:
 1. A vulcanizable, fluorine-containing elastomercomposition which comprises a fluorine-containing elastomer having cyanogroup as cross-linkable groups and a bisaminothiophenol compoundrepresented by the following general formula I!: ##STR4## wherein Rf isa perfluoroalkylidene group having 1 to 10 carbon atoms.
 2. Avulcanizable, fluorine-containing elastomer composition according toclaim 1, wherein the bisaminothiophenol compound is2,2-bis(4-amino-3-mercapto-phenyl)hexafluoropropane.
 3. A vulcanizablefluorine-containing elastomer composition according to claims 1 or 2,wherein the fluorine-containing elastomer is a terpolymer comprisingtetrafluoroethylene, perfluoro(lower alkyl vinyl ether) orperfluoro(lower alkoxy-lower alkyl vinyl ether) and perfluorounsaturated nitrile compound.